The present invention relates to a method for discharging an electrochemical cell and, more particularly, to a method for internally discharging a primary electrochemical cell following the premature cessation or significant decline in the discharge of the cell due to a break or other impairment of internal electrical connections of the cell.
Primary electrochemical cells are commonly available in a large assortment of sizes and shapes. One type of primary electrochemical cell which has been particularly successful, especially for high-current drain, low-temperature applications, is a so-called prismatic cell. Such a cell is generally described in U.S. Pat. No. 4,086,397, in the names of Franz Goebel and Nikola Marincic, and includes a physically large battery stack enclosed together with an electrolytic solution within a large, generally-rectangular metal housing. The battery stack as used within the cell comprises a large number of generally-rectangular cell components including a plurality of anodes, carbon cathode current collector electrodes, and insulative separators between the anodes and the carbon cathode current collector electrodes. Each anode generally comprises a large rectangular sheet of an oxidizable alkali metal, such as lithium, physically impressed into a supporting (e.g., nickel) grid, and each of the carbon cathode current collector electrodes comprises an aggregation of porous, semi-rigid carbon globules or conglomerates physically impressed into a metal (e.g., nickel) current collector grid. Each of the anodes and carbon cathode current collector electrodes further has a narrow rail around the periphery thereof and a tab connected to the rail for facilitating the physical and electrical connection of the associated electrode to a corresponding terminal assembly. A common and preferred electrolytic solution employed in the cell as described above is a cathodelectrolyte solution comprising a reducible soluble cathode such as thionyl chloride and an electrolyte solute such as lithium tetrachloroaluminate dissolved in the thionyl chloride.
By the appropriate selection of the battery cell components, a cell as described above can be constructed to have any one of several possible sizes and energy configurations. A typical cell, for example, has exterior dimensions of approximately 18 inches (height).times.13 inches (width).times.10 inches (depth), a weight of 156 pounds, an ampere-hour capacity rating of 10,000 ampere-hours, and a nominal discharge current of 40 amperes.
During the normal discharge of the cell as described hereinabove, current is drawn from the cell by way of its externally-located terminals, or posts, and supplied to a load coupled to the terminals. It is normally expected that the cell will be useful in supplying current to the load until the cell has become fully discharged, a condition which occurs when one or more active components of the electrochemical system of the cell has been fully consumed by chemical reaction within the cell during discharge. However, in the event the external electrical circuit of the cell is interrupted or otherwise impaired for any reason during discharge of the cell, such as an open circuiting of one or more of the internal electrical connections between cell terminals and the anodes and/or carbon cathode current collector electrodes, the discharge of the cell prematurely discontinues or the discharge is significantly diminished. In such a situation, and especially where a high amount of energy may still remain in the cell, it is highly desirable that the discharge of the cell be completed in some safe and expeditious fashion so as to facilitate the ultimate disposal of the cell. Since, as indicated above, the cell can no longer be effectively discharged by way of the cell terminals, clearly some other solution is required.